A suitable self-healing tire puncture sealant must withstand wintertime temperatures to which tires are subjected when standing idle. Such a sealant must also withstand the high temperatures to which tires are heated under summertime driving conditions. These temperatures typically range from -20.degree. F to 270.degree. F. A suitable tire sealant must be capable of sealing punctures when the puncturing object is retained in the tread and also when the puncturing object is removed. Thus, a tire sealant must be capable of adhering to the puncturing object as it works against a flexing tire during travel and must be capable of adhering to itself to seal the puncture after removal of the puncturing object. In addition, the sealant must remain effective for an extended period of time. These conditions require a combination of flexibility, tackiness and strength that are among the most demanding required of any sealant composition. Finally, a suitable tire sealant must be susceptible to economical formulation and application.
Because butyl rubber exhibits low air permeability and high resistance to aging, the prior art has attempted to utilize butyl rubber as a basic compound of sealants. Exemplary of such prior art are U.S. Pat. Nos. 2,756,801, 2,765,018 and 2,782,829. Methods of applying such sealants have included one in which the sealant is solvated, sprayed on to the inner surface of the tire, and allowed to cure in situ. In another method, it is cured in sheet form and then applied to the tire. Whatever the method, short gel times and cure times are important to the realization of production economies.
The gel time takes on a special importance in the spray application technique because the sprayed sealant, before gelling, tends to flow under its own weight. The result is that there is a maximum thickness of sealant, dependent on the gel time, which can be applied in one spraying operation. Despite the use of heat, thixotropes, centrifugal force and other techniques, this maximum thickness has previously been less than the thickness of sealant required for a self-healing tire. Multiple spraying/curing operations have therefore been necessary.